A lathe is a machine that shapes a workpiece, which may be any solid material, e.g., wood, plastic or metal, generally by turning the workpiece against stationary, changeable tools; and mills and routers are machines that shape a workpiece generally by turning changeable tools against a stationary workpiece.
Both types of machines are commonly provided with “computer numerical control,” which provides for programmed control of the turning and the changing of tools, so that the workpiece can be worked with minimum operator intervention. Herein, CNC lathes, routers and mills will be referred to generically as CNC machines or CNC machining tools.
In lathes, the tool is stationary and the workpiece spins. Provision for changing tools in a CNC lathe is by use of a “turret,” which is a receiver that can hold multiple tools. The turret is radially indexably motor-driven to select the desired tool, and is axially motor-driven to bring the tool against the spinning workpiece.
The tools are mounted for receipt by the turret in specialized “tool-holders” that are designed to mate the particular tool to the particular CNC machine. Such tool-holders are typically provided by the manufacturer of the CNC machine.
In standard CNC routers and mills, the workpiece is mounted to a table that is motor-driven to allow for translating the workpiece, with reference to a standard x, y, z coordinate system, in the x and y axes, and the tool spins about the z axis. Tools are again mounted in specialized tool-holders. But in this case a selected tool-holder/tool combination is removed from a library and carried to a spindle by an “automatic tool changer” or “ATC,” which also removably mounts the tool-holder/tool to the spindle. The spindle is motor-driven for spinning the tool, and for translating the tool along the z axis so as to bring it into contact with the workpiece.
Some CNC lathes provide for spinning the tools as well, and can thereby perform the same operations as a CNC router or mill. In addition, some CNC machines allow for orienting and translating tools at arbitrary angles relative to the workpiece.
For machining metal workpieces formed of metal, CNC machines typically provide for continuous irrigation of the interface between the workpiece and the tool that is being used to shape the workpiece with a “cutting fluid,” which is a fluid designed specifically for metalworking and machining processes, which provides for both cooling and lubricating the workpiece and the tool. The cutting fluid is recycled from a sump that typically holds 20 gallons or more of cutting fluid.
Cutting fluids are selected as a trade-off between cooling and lubricity; water-based cutting fluid providing better cooling and oil-based cutting fluid providing better lubricity. It is impractical to change the cutting fluid during the time that a workpiece is being machined; therefore, the trade-off cannot for practical purposes be optimized for each machining operation. Accordingly, when greater lubricity is needed, such as when tapping tough stainless steel, the operator of the CNC machine will typically need to intervene by stopping the machine and manually applying an alternative cutting fluid that is better suited to the particular machining operation. For example, for a tapping operation, this means manually injecting the fluid into the hole to be tapped.